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<h2><span class="refentrytitle">Macro BOOST_CONTRACT_OLDOF</span></h2>
<p>BOOST_CONTRACT_OLDOF — Macro typically used to copy an old value expression and assign it to an old value pointer. </p>
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<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis"><span class="comment">// In header: &lt;<a class="link" href="reference.html#header.boost.contract.old_hpp" title="Header &lt;boost/contract/old.hpp&gt;">boost/contract/old.hpp</a>&gt;

</span>BOOST_CONTRACT_OLDOF(...)</pre></div>
<div class="refsect1">
<a name="idm42655"></a><h2>Description</h2>
<p>The expression expanded by this macro should be assigned to an old value pointer of type <code class="computeroutput"><a class="link" href="boost/contract/old_ptr.html" title="Class template old_ptr">boost::contract::old_ptr</a></code> or  <code class="computeroutput"><a class="link" href="boost/contract/old_ptr_if_copyable.html" title="Class template old_ptr_if_copyable">boost::contract::old_ptr_if_copyable</a></code>. This is an overloaded variadic macro and it can be used in the following different ways.</p>
<p>1. From within virtual public functions and public functions overrides:</p>
<pre class="programlisting"><span class="identifier">BOOST_CONTRACT_OLDOF</span><span class="special">(</span><span class="identifier">v</span><span class="special">,</span> <span class="identifier">old_expr</span><span class="special">)</span>
</pre>
<p>2. From all other operations:</p>
<pre class="programlisting"><span class="identifier">BOOST_CONTRACT_OLDOF</span><span class="special">(</span><span class="identifier">old_expr</span><span class="special">)</span>
</pre>
<p>Where:</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p><code class="computeroutput"><span class="bold"><strong>v</strong></span></code> is the extra parameter of type  <code class="computeroutput"><a class="link" href="boost/contract/virtual_.html" title="Class virtual_">boost::contract::virtual_</a></code><code class="computeroutput">*</code> and default value <code class="computeroutput">0</code> from the enclosing virtual public function or public function overrides declaring the contract. </p></li>
<li class="listitem"><p><code class="computeroutput"><span class="bold"><strong>old_expr</strong></span></code> is the expression to be evaluated and copied into the old value pointer. (This is not a variadic macro parameter so any comma it might contain must be protected by round parenthesis and <code class="computeroutput">BOOST_CONTRACT_OLDOF(v, (old_expr))</code> will always work.)</p></li>
</ul></div>
<p>
On compilers that do not support variadic macros, programmers can manually copy old value expressions without using this macro (see  <a class="link" href="boost_contract/extras.html#boost_contract.extras.no_macros__and_no_variadic_macros_" title="No Macros (and No Variadic Macros)"> No Macros</a>).</p>
<p><span class="bold"><strong>See Also:</strong></span></p>
<p> <a class="link" href="boost_contract/tutorial.html#boost_contract.tutorial.old_values" title="Old Values"> Old Values</a> </p>
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